2. Acute mesenteric ischemia is a common but
complex disorder with various primary cause and
clinical presentation and high mortality.
Can be caused by various conditions such as arterial
occlusion, venous occlusion, strangulating
obstruction and hypoperfusion associated with
nonocclusive vascular disease
3. Findings vary widely depending on the cause and
underlying pathophysiology.
The severity of bowel ischemia (i.e. superficial mucosal or
transmural bowel wall necrosis)
Location (i.e., small or large bowel)
Degree of hemorrhage subsequent super infections may
affect the CT appearance.
4. Preparation:-
Oral and rectal administration of contrast material is
recommended for accurate CT and assessment of acute
bowel ischemia.
Whether contrast material is indicated should be carefully
considered for patients with bowel obstruction;
Materials containing barium are contraindicated in
patients with bowel leak or perforation.
However, in the acute state, particularly life-threatening
conditions, indication of transoral contrast may not be
possible or may not be significant because of an adynamic
ileus preventing contrast material from moving through
the intestine.
5. Neutral contrast material should be used for the correct
assessment of bowel enhancement after IV contrast
administration.
The use of neutral contrast material is also beneficial in the
formation of multiplanar images and in CT angiography
because neutral contrast material does not interfere with
image quality.
Positive contrast material used in assessing patients with
ischemic colitis by showing thickened bowel wall and
revealing the presence of bowel obstruction
Or in evaluating patients with a contraindication for IV
contrast administration.
6. When contrast material is applied, oral administration of
600–750 mL of luminal contrast material 30–120 minutes
before scanning and rectal administration of 400–800 mL of
luminal contrast material are used.
7. CT images are obtained from the dome of the liver to the level of
the perineum to cover the entire course of the intestine.
With MDCT scanners,
Collimation of 0.5–2.5 mm
Detector pitch of 1.0–2.
Section thickness - 5- to 7-mm are usually constructed for image
interpretation;
8. Acquisition of both unenhanced and contrast enhanced CT scans
is always necessary.
Role of unenhanced CT is to identify vascular calcification, hyper
attenuating intravascular clotting, and intramural hemorrhage.
CECT is to identify thrombi in the mesenteric arteries and veins,
abnormal enhancement of the bowel wall, and the presence of
embolism or infarction of other organs.
100–150 mL of iodinated contrast material
Rate - 2–5 mL/s,
scanning starts with delay times of 30 and 60 seconds for
dual acquisition and 40 – 60 seconds for single acquisition.
9. • Variations depend on
- Pathogenesis of bowel ischemia
- Acuteness,
- Duration, site, and extent of the ischemic attack
- State of the collateral circulation
- Superimposed bowel wall infection
- Presence of perforation may also affect appearances
of acute bowel ischemia.
10. Normal ranges from 3 to 5 mm thick depending on
the degree of bowel distention.
It is non specific but is the most frequently
observed finding in mesenteric ischemia ,caused by
mural edema, hemorrhage, or super infection of the
ischemic bowel wall .
The degree of thickening is usually less than 1.5 cm,
typically 8–9 mm.
Often observed in mesenteric venous occlusion,
strangulation, ischemic colitis, and mesenteric
arterial occlusion after reperfusion.
11. In arterial occlusive mesenteric ischemia ,the bowel
wall becomes thinner rather than thicker
Because there is no arterial flow and neither mural
edema nor hemorrhage occurs.
Thinning of the bowel wall or “paper-thin wall” is
caused by volume loss of tissue and vessels in the
bowel wall and by loss of intestinal muscular tone.
Bowel wall thickening is not a consistent finding in
mesenteric ischemia, and the degree of thickening
does not correlate with severity.
12.
13. Always be assessed on both unenhanced and contrast-enhanced
CT images to avoid misinterpretation of high density of the
bowel wall as normal positive enhancement on contrast-
enhanced CT in cases of intramural hemorrhage.
On unenhanced CT images -
low attenuation of the bowel wall indicates bowel wall
edema, occurs in mesenteric arterial occlusion after
reperfusion, mesenteric venous occlusion, strangulation,
and ischemic colitis.
14. High attenuation of the wall is caused by intramural
hemorrhage and hemorrhagic infarction.
On CECT -
a highly specific but not sensitive finding for acute
mesenteric ischemia is absent or diminished contrast
enhancement of the bowel wall .
A halo or target appearance is also indicative of
mesenteric ischemia, representing hyperemia and hyper
perfusion associated with surrounding mural edema.
Can be seen in arterial occlusion after reperfusion,
nonocclusive and veno-occlusive bowel ischemia,
strangulation, and ischemic colitis.
15.
16.
17. In the setting of mesenteric ischemia, Pneumatosis
often indicates transmural infarction, particularly if
it is associated with portomesenteric venous gas.
18.
19.
20. Dilated because of interruption of normal bowel
peristalsis (adynamic ileus).
Fluid distention of the bowel loops occurs by
increased intestinal secretions, typically in veno-
occlusive ischemia and strangulating bowel
obstruction.
In exclusive arterial occlusion, the bowel seldom
contains a large amount of luminal fluid.
21. In most cases, emboli or thrombi in the mesenteric
arteries and veins are clearly shown on contrast-
enhanced CT images
Engorgement of the mesenteric veins caused by
congestion of venous outflow is typically seen in
venoocclusive bowel ischemia or strangulating
bowel obstruction.
22. Mesenteric fat stranding and ascites appear with transudation
of fluid in the mesentery or the peritoneal cavity caused by
elevation of mesenteric venous pressure, which is commonly
seen in strangulating bowel obstruction and venoocclusive
bowel ischemia.
It is also frequently seen in ischemic colitis because of super
infection of ischemic colonic segments.
mesenteric fat stranding in these conditions can appear
without bowel infarction and has limited value in estimating
the severity of bowel ischemia.
23. Patients with arterial occlusive mesenteric ischemia,
because the CT finding of fat stranding is almost exclusively
present with transmural infarction.
24. Bowel ischemia and infarction can be caused by
various conditions such as
mesenteric arterial occlusion
mesenteric venous occlusion
strangulating bowel obstruction and
hypo perfusion associated with nonocclusive vascular
disease.
25. Caused by aThromboembolism associated with cardiovascular
problems followed by arterial thrombosis, which accounts for
arterial embolism, 40–50%;
arterial thrombosis, 20–30%.
Most emboli wedge at branching points around or distal to the
middle colic artery, whereas thrombosis typically occurs at or
near the origin of the mesenteric arteries.
Although the severity may vary, bowel ischemia is typically
followed by infarction, perforation, and peritonitis unless
reperfusion occurs.
26. On CECT images, emboli and thrombi can be seen as defects in
the superior mesenteric artery and its branches.
The diameter of the superior mesenteric artery is often larger
than that of the superior mesenteric vein.
The thickness of the bowel wall of the involved segments is the
same as or thinner than that of the healthy segments unless
reperfusion occurs.
The lumen of the bowel may be filled with fluid, gas, or both;
however, the bowel seldom contains a large amount of fluid.
Contrast enhancement of the involved bowel is absent or
diminished.
27.
28. Pneumatosis can typically be observed in cases with
transmural infarction with or without associated
portomesenteric venous gas.
In cases with reperfusion or rich collaterals, the involved
bowel segments may thicken and show the halo or target
pattern of contrast enhancement.
29.
30. Thrombosis of the mesenteric vein can be primary or
secondary to portal hypertension or infection or can
be associated with various hypercoagulopathy
states.
Mesenteric venous obstruction does not typically
lead to severe bowel ischemia; however, thrombosis
of the mesenteric vein, particularly at a distal level,
may cause bowel infarction and
Accounts for 5–10% of acute bowel ischemia
31. Elevation of the hydrostatic pressure, which leads to
extravascular leakage of plasma, RBCs, or both into the bowel
wall, mesentery, and peritoneal cavity.
The bowel loops are typically prominently dilated.
Impairment of venous drainage may also compromise the
arterial blood flow and cause bowel ischemia and infarction.
On CECT, thrombus in the mesenteric and portal veins is usually
visible, and mesenteric venous obstruction can be confirmed by
CT in more than 90% of cases.
32. Engorgement of the mesenteric veins is also observed.
Fat stranding in the mesentery and ascites are common
findings.
The bowel wall is prominently thickened with absent or
diminished enhancement, hyperenhancement, or a halo or
target pattern of contrast .
Absent or diminished contrast enhancement of the bowel wall
usually indicates transmural infarction,
Particularly when it is associated with pneumatosis and
portomesenteric venous gas .
33.
34. Mechanical bowel obstruction associated with bowel
ischemia that is seen in approximately 10% of patients with
small-bowel obstruction.
Strangulating obstruction is almost exclusively associated
with a closed-loop obstruction.
Which is caused most often by an adhesive band and
occasionally by an internal or external hernia. A closed-loop
obstruction tends to involve the mesentery and mesenteric
vessels and is prone to produce a volvulus.
35. Strangulation in a closed-loop bowel obstruction is
caused
initially by impairment of venous outflow followed by
arterial ischemia because the arterial pressure is
higher than the venous pressure.
Congestion or hemorrhage in the bowel wall and
mesentery occurs, and the affected bowel loops are
distended and filled with fluid.
36. On CT, a closed-loop obstruction is identified by a unique
configuration of C- or U shaped distended loops with the
mesenteric vessels converging toward the site of obstruction.
The obstructed site of the closed loops can be located by
following the course of the distended bowel loops.
The affected bowel is filled almost exclusively with only fluid
and no gas.
The affected mesentery typically shows a fan shape.
37.
38.
39. absent or diminished bowel wall enhancement and
infiltration of the affected mesentery are highly
specific.
The “small-bowel feces sign” is also reported as a
useful finding indicating the presence of
strangulation.
40. Bowel ischemia and infarction can occur with a reduction of
mesenteric blood supply without vascular occlusion, which is called
nonocclusive mesenteric ischemia or infarction.
This type of bowel ischemia accounts for 20–30% of all acute
mesenteric ischemia or infarction cases, with mortality rates
fromn30% to 93%
A reduction of the mesenteric blood supply is the result of
mesenteric arterial vasoconstriction on reflex to hypotension or
administration or abuse of digitalis, ergotamine, vasopressin or
other vasoconstrictive agents, amphetamine, and cocaine.
41. Ischemic injury may range from reversible superficial
damage localized to the watershed areas to a more severe
form that extends to the entire bowel.
Hypoperfusion results in increased vascular permeability
that leads to extravascular leakage of plasma, RBCs, or both
into the bowel wall, mesentery, and peritoneal cavity.
Shock bowel is a variation of nonocclusive mesenteric
ischemia caused by hypotensive shock induced by blunt
abdominal trauma.
Ischemic colitis and obstructive colitis are considered
similar disease entities.
42. On CT, the bowel wall of the involved segments may be
normal or thickened.
The pattern of enhancement is variable as absent or
diminished enhancement, increased enhancement, or halo
or target type of enhancement.
Fat stranding of the mesentery and ascites are visible.
nonocclusive mesenteric ischemia is the most difficult
condition to diagnose on CT, and angiography is often required
for correct and confident diagnosis
